Change alpha level of geom_point in legend on top of stat_smooth

Question

I'm running into trouble changing the alpha of my (coloured) points in the legend when I add stat_smooth.

require(ggplot2)

set.seed(1052)
dx <- runif(2000,0,10)
dy <- dx * rep(c(1,-1), each = 1000) + rnorm(2000,0,1)
dcol <- rep(c(TRUE, FALSE), each = 1000)
dd <- data.frame(x = dx, y = dy, col = dcol)

gg <- ggplot(dd) + aes(x = x, y = y, colour = col) + geom_point(alpha = 1/5)
gg

The alpha of the points carries over to the legend (making the colours hard to view), but this question shows that you can override legend details with guides:

magic <- guides(colour = guide_legend(override.aes = list(alpha = 1))) 
gg + magic

Cool. But when I throw in stat_smooth, the magic stops working.

gg + stat_smooth(method = "lm")

gg + stat_smooth(method = "lm") + magic

How can I fix this? I would rather have the below result for the legend (white background, line and point with alpha = 1. (The issues seems to go away if you use geom_line and not stat_smooth)

gg + geom_line(alpha = 1/10) + magic

Answer 1

If you want to get legend key with just line and point and without background then you can add fill=NA inside the override.aes= - this will remove grey fill of legend key that is set due to confidence intervals of stat_smooth() (se=TRUE). Then with theme() and legend.key= you can change background to white.

ggplot(dd, aes(x = x, y = y, colour = col)) + geom_point(alpha = 1/5)+
  stat_smooth(method = "lm")+
  guides(colour = guide_legend(override.aes = list(alpha = 1,fill=NA))) + 
  theme(legend.key=element_rect(fill="white"))